Morphological study on early ontogeny of theGinkgo leaf

The early ontogeny of theGinkgo leaf was studied by scanning electron microscope. The lamina of the leaf is derived from the protuberance of the adaxial side of a leaf buttress. The protuberance shows successive bifurcations. The second bifurcation occurs approximately at a right angle to the first. Thus, the abaxial surface of the leaf is derived from the outer surface of the protuberance and the adaxial is derived from the depressed inner surface of the protuberance formed by the first and second bifurcations. It is supposed that thick veins along both edges of the lamina are differentiated by an uneven dichotomous branching system of procambia caused by positional relationships: both edges of the lamina are derived from the parts of the protuberance just above a pair of procambia which come from the stem. On the shoot apex, there are a central cell group, which consists of only a few cells, and radially-arranged cell files. The leaf primordium is initiated from a sector area which consists of several files among radially-arranged cell files.